Nasal and full-face masks systems suitable for the delivery of air or other breathable gases to patients for the treatment of sleep disordered breathing may include a mask (100), a forehead support (120) and headgear (140), as depicted in FIG. 1. The mask may comprise a rigid shell (160), termed a frame, and a soft portion (180), termed a cushion. The frame may be constructed from a material such as polycarbonate, forming a cavity which overlies the patient's nose and/or mouth. The soft cushion may be constructed from a material such as silicone spacing the frame away from the patient's face to provide comfortable contact.
In the case of the Mirage® Mask (ResMed Limited), shown in FIG. 1, the headgear (140) is constructed from fabric and includes a rear portion which engages the region near the occiput of the patient, and four straps (145) which are secured to a forehead support (2 straps) and nasal mask frame (2 straps). The straps include hook and loop material, such as Velcro™ on one side. The mask frame and forehead supports include loops through which straps can pass.
In one form of known mask, the cushion and frame are glued together, as shown in FIGS. 2a to 2c. FIG. 2c shows a cross-section 2c-2c through FIG. 2a. The frame (160) includes a rim portion (200) surrounding the rear aperture of the frame. There is a corresponding rim portion (220) on the cushion (180) which fits inside the rim (200) on the frame. The two rims (200, 220) are glued together. A disadvantage with this approach is that the cushion cannot easily be removed for separate cleaning from the frame. Furthermore, there is an increased manufacturing cost since gluing requires assembly time and adhesive.
In one known mask, the Modular mask system (ResMed Limited), the frame and cushion are held, together using a tongue (300) and groove (320), as depicted in FIGS. 3a to 3c. The frame (160) is generally triangular in front view. In use, the front of the frame faces away from the patient and the back of the frame faces towards the patient. The rim portion (350) on the frame (160) includes an outwardly extending flange (340) and engages with a corresponding rim (360) on the cushion (180), such that the rims (350, 360) confront along a locus lying generally in the plane of the patient's face. The frame rim (350) further includes a tongue (300) which protrudes rearwardly from the back of the frame and is received in a corresponding complementary shaped groove (320) formed in rim portion (360) of the cushion (180). In addition, the rim (350) of the frame (160) and the rim (360) of the cushion (180) include aligned slots (380) through which headgear straps (145) can pass. Hence the slots (380) and straps (145) make a contribution to holding the frame (160) and cushion (180) together, in addition to the use of the tongue (300) and groove (320).
In another known mask, a tongue and groove mechanism is used to hold the frame (160) and cushion (180) together, and the tongue (500), which is positioned on the frame (160) has an irregular cross-section as depicted in FIGS. 4a to 4c. The side (520) of the tongue (500) on the interior of the frame (160) is flat. The other side (540) of the tongue (500) has a lateral projection (560) approximately at right angles to the tongue (500). The groove (580) of the cushion (180) has a complimentary shape, including a lateral recess (585) for receiving projection (560). The connection relies on the elasticity of the cushion to retain the cushion in place.
The present invention aims to provide an improved arrangement.